1. Field of the Invention
This invention relates generally to methods and apparatus related to the polishing of workpieces, such as semi-conductor wafers, and particularly to an improved pad or disk for conditioning and restoring polishing pads used in such methods.
2. Description of the Related Art
The production of integrated circuits involves the manufacture of high quality semiconductor wafers. As well known in this industry, a high precision, flat or planar surface is required on at least one side of the wafer to assure appropriate performance objectives are attained. As the size of the circuit components decrease and the complexity of the microstructures involved increase, the requirement for high precision surface qualities of the wafer increases.
In order to meet this need, the polishing pads typically used in the industry require re-conditioning to restore their original configuration after a period of use so that the pad may continue to be used to provide the desired surface on the wafers. The chemical, mechanical planarization or polishing processes and apparatus used are well known. Reference to prior Holzapfel et al. U.S. Pat. No. 4,805,348 issued February, 1989; Arai et al. U.S. Pat. No. 5,099,614 issued March, 1992; Karlsrud et al. U.S. Pat. No. 5,329,732 issued July, 1994; Karlsrud et al. U.S. Pat. No. 5,498,196 issued March, 1996; Karlsrud et al. U.S. Pat. No. 5,498,199 issued March, 1996; Cesna et al. U.S. Pat. No. 5,486,131 issued January, 1996; and Holzapfel et al. U.S. Pat. No. 5,842,912 issued Dec. 1, 1998, provide a broad discussion of chemical, mechanical planarization referred to herein and in the industry as CMP processes.
During the polishing or planarization process of the semiconductor wafers, the polishing pad is rotated against the wafer in the presence of an abrasive slurry. The polishing pad generally used comprises a blown polyurethane-based material such as the IC and GS series of pads available from Rodel Products Corporation located in Scottsdale, Ariz. The hardness and density of the polishing pads depends upon the material of the workpiece (semiconductor wafer) that is to be polished.
During the CMP process, the chemical components of the abrasive slurry used tend to react with one or more particular materials on the wafer being polished and aid the abrasive in the slurry to remove portions of this material from the surface. During continued use of the polishing pad in this process, the rate of material removal from the wafer gradually decreases due to what is referred to in this field as “pad glazing”. Additionally, with continued use, the surface of the polishing pad likely experiences uneven wear which results in undesirable surface irregularities. Therefore it is considered necessary to condition (true and dress) the polishing pad to restore it to a desirable operating condition by exposing the pad to a pad conditioning disk having suitable cutting elements. This truing and dressing of the pad may be accomplished during the wafer polishing process (in-situ conditioning) such as described in U.S. Pat. No. 5,569,062 issued on Oct. 29, 1996 to Karlsrud. However, such conditioning may also be done between polishing steps (ex-situ conditioning) such as described in U.S. Pat. No. 5,486,131 issued on Jan. 23, 1996 to Cesna et al., both of these patents being incorporated by reference herein.
Appropriate conditioning of the polishing pad is essential to restore the appropriate frictional coefficient of the pad surface and to allow effective transport of the polishing slurry to the wafer surfaces in order to obtain the most effective and precise planarization of the semiconductor wafer surface being polished.
The pad conditioner typically employed comprises a stainless steel disk coated with a monolayer of abrasive particles. Typically diamond particles or cubic boron nitride particles are preferred. These superabrasive particles may be secured to the conditioning disk by electroplating or by a brazing process. The braze bond has become more preferred due to forming a stronger bond between the diamond particles and substrate such that the diamond particles are less likely to loosen and fall free compared to electroplated conditioning disks. If such loose abrasive particles become embedded in the polishing pad or otherwise exposed to the wafer being polished, serious deformations in the wafer surface may occur such that the wafer becomes unusable and represent a loss of many thousands of dollars of time and labor.
Conditioning disks employing a monolayer of braze bonded diamonds, such as manufactured by Abrasive Technology, Inc. of Lewis Center, Ohio, have been recognized as very effective and an improvement over prior art conditioning disks using other bonding mediums, particularly in resisting premature loss of diamond abrasive particles. However, the corrosive nature of the polishing slurries currently used and the nature of even more aggressively corrosive slurry compositions which may be deemed more desirable for the CMP processes, present a problem which tends to shorten the useful life of even such braze bonded conditioning disks. These highly acidic polishing slurries attack the metallic bonding medium and the metal substrate. This action tends to cause premature loss of superabrasive particles and the undesirable effect resulting therefrom. This tendency has led those skilled in this art to employ various coatings over the superabrasive particles and the metallic bonding medium and/or the substrate. Some prior attempts of this nature are disclosed in U.S. Pat. No. 6,517,424 and in some of the cited references noted therein, each being incorporated by reference. However, the CMP industry has not fully accepted this solution, and a more satisfactory solution has eluded those of ordinary skill in the art.